Colorectal cancer is among the leading causes of cancer-related morbidity and mortality in industrialized nations. The pathogenesis is related to hereditary influences, modified by the quantity and quality of dietary fat. In 1995, the American Cancer society estimated that 135,000 new cases of colon cancer were diagnosed; 71% were in the colon and 30% were in the rectum. Patients diagnosed at an early stage, prior to lymph-node spread, are potentially cured with surgery. Approximately 40% of patients are diagnosed at an early stage. The remaining cases frequently undergo peri-operative radiation and/or chemotherapy to attempt to control the metastatic spread of disease. Ultimately, 50% of patients thought to have undergone curative resections eventually develop recurrent disease. Unfortunately, 55,000 Americans die each year due to recurrent or metastatic colon or rectal cancer. The key to enhanced survival is early diagnosis. Colon and rectal cancers are often silent and slowly progressive. Most patients exhibit symptoms such as rectal bleeding, pain, abdominal distension or weight loss only after the disease is advanced and not surgically curable.
Early detection depends upon availability of high-quality methods. Such methods are also useful for determining patient prognosis, selecting therapy, monitoring response to therapy and selecting patients for additional therapy. Although methods for detecting colon cancer exist, the methods are not ideal. Digital rectal exams (i.e., manual probing of rectum by a physician), for example, although relatively inexpensive, are unpleasant and can be inaccurate. Fecal occult blood testing (i.e., detection of blood in stool) is nonspecific because blood in the stool has multiple causes. Colonoscopy and sigmoidoscopy (i.e., direct examination of the colon with a flexible viewing instrument) are both uncomfortable for the patient and expensive. Double-contrast barium enema (i.e., taking X-rays of barium-filled colon) is also an expensive procedure, usually performed by a radiologist. Consequently, there is a need for cancer diagnostic methods that are specific, accurate, minimally invasive, technically simple and inexpensive.
Because of the disadvantages of existing methods for detecting or treating cancers, new methods are needed for cancer diagnosis and therapy.